NAME
POE::Component::PreforkDispatch - Preforking task dispatcher
DESCRIPTION
Applications that require lots of asynchronous tasks going at once may
suffer a performance hit from repeating the fork/die process over and
over again with each enqueued job. Similar to how Apache forks, this
dispatcher will maintain a pool of available forks and a queue of
pending tasks. Each task (request) will be handled in turn, and will
return to the callback when done.
SYNOPSIS
use POE qw(Component::PreforkDispatch);
POE::Session->create(
inline_states => {
_start => \&start,
do_slow_task => \&task,
do_slow_task_cb => \&task_cb,
},
);
$poe_kernel->run();
sub start {
POE::Component::PreforkDispatch->create(
max_forks => 4,
pre_fork => 2,
);
foreach (1..5) {
print "Enqueued request $_\n";
$poe_kernel->post(PreforkDispatch => 'new_request', {
method => 'do_slow_task',
upon_result => 'do_slow_task_cb',
params => [ 'a value', $_, ],
});
}
}
sub task {
my ($kernel, $heap, $from, $param1, $param2) = @_[KERNEL, HEAP, ARG0 .. $#_];
# ... do something slow
print STDERR "Task running with '$param1', '$param2'\n";
sleep 10;
# Return hashref or arrayref
return { success => 1 };
}
sub task_cb {
my ($kernel, $heap, $request, $result) = @_[KERNEL, HEAP, ARG0, ARG1];
print STDERR "Task with param ".$request->{params}[1]." returned "
.($result->{success} ? 'successful' : 'failure')."\n";
}
USAGE
Methods
Constructor
Call ->create() like with any other "POE::Session", passing a list of
named parameters.
* methods => \%methods
* classes => \@classes
* xmlrpc_server_parent => $session_name
Provide an optional means of finding a method to dispatch a request
to. If none are provided, the request itself needs to indicate it's
method.
methods => {
'do_something' => \&do_something,
'do_else' => 'do_else_state',
},
Methods will be searched for by name and will call either the state
or the subroutine. See below for how either is called.
classes => [ 'My::Class' ],
Methods will be attempted in each namespace provided, and called as
subroutines.
xmlrpc_server_parent => 'XMLRPC_Session_Alias',
Requests will be wrapped in a pseudo-transaction capable of being
passed onto a POE::Component::Server::XMLRPC session for handling.
* upon_result => $subref || $state_name
If provided, used as a fallback result function to send completed
requests to.
* max_forks => $num
Number of forks, max, to spawn off to handle requests.
* pre_fork => $num
How many forks to start out with. The rest are spawned as needed,
with a 2 sec delay between new forks.
* max_requests => $num
How many requests each fork can handle before being slayed and
respawned (if necessary).
* verbose => $num (defaults 0)
* talkback => sub { }
The dispatcher logs certain events, and can be verbose about it. The
talkback function will be passed a single arg of a log line. This
defaults to printing to STDOUT.
* fork_name => $name
In process lists on a POSIX system, you can change the name of the
forked children so you can at a glance know that they're dispatcher
forks and not the parent process. Will be renamed to "$name child".
* alias => $session_name
Provide a session name. Defaults to 'PreforkDispatch'.
Session States
new_request (\%param)
The primary interface to enqueueing requests. Takes the following
arguments in a hashref.
$poe_kernel->post( PreforkDispatch => 'new_request', {
method_name => 'do_something',
params => [ 'Computer 3' ],
});
* method_name
Provide a method name for searching for an appropriate method to
dispatch to. Most akin to XMLRPC's method_name.
* method => $subref || $session_state
Instead of using the method_name, you can provide the method session
state or subref to use as a request handler.
* upon_result => $subref || $session_state
Instead of using the global upon_result, provide a per-request
callback.
* params => $arrayref
An arrayref, this is where you put your payload of the request.
* from
An XMLRPC value, this is not used typically for a single-host
application.
Request to response
After a new_request() is issued, the dispatcher will process it in a
FIFO queue, using forks if available, or handling it synchronously
otherwise. Handling a request is done by searching for a valid method,
either picking the $request->{method}, or if not available, searching
the dispatcher methods, classes and finally the xmlrpc_server_parent for
something to handle $request->{method_name}.
If the method given is a subref, it will be passed ($from, @args). If a
POE session state name, the calling session will have this state posted
to with the same args ($from, @args):
my ($from, @args) = @_;
or
my ($kernel, $heap, $from, @args) = @_[KERNEL, HEAP, ARG0 .. $#_];
Once the request is handled, successfully or not, a response is sent to
either the request's 'upon_result', or the dispatchers. If the method is
a subref, it will be handed ($request, $response). Similar for session
state. The request will be the same as passed, but with the additional
key/value of 'elapsed' containing the seconds the request took to
process. The response will be the response value of the method that
handled the request, or in the case of an error, a hashref with the key
'error'.
Special methods
There are some methods that are special and can be used to control child
fork behavior
* _precall
* _postcall
Not sure if these are useful, but will be called before and after
the named method. Can be used as universal constructor/destructors
for method calls. Passed the main method params.
* _fork_preinit
* _fork_postinit
Code to be called before and after actually forking (in the parent
process).
* _fork_init
Not passed anything, this permits the fork to do something that's
better done after forking (opening handles and such).
SEE ALSO
POE, POE::Component::Pool::Thread, POE::Component::JobQueue
TODO
* Class-based method discovery
* More tests
AUTHOR
Eric Waters
COPYRIGHT
Copyright (c) 2007 Eric Waters and XMission LLC
(http://www.xmission.com/). All rights reserved. This program is free
software; you can redistribute it and/or modify it under the same terms
as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.